1. Field of the Invention
This invention relates to a current consumption control device for suppressing consumption of current supplied from a power supply such as a battery in a car.
2. Description of the Related Art
Recently, the technique of electronically controlling the running system of a motorcar including an engine has been developed. For control of the running system and the like, data communication inside the car is effected by use of, for example, a LAN system or the like in which a plurality of nodes are connected to a network. In such a data communication system, the power supply is obtained from a battery. Therefore, in order to operate the communication system while the engine is stopped, it is desirable to suppress the current consumption of the battery while the network communication is not effected so as to set the current consumption as low as possible.
Conventionally, in this type of device, a voltage supplied from the power supply is stabilized by a power supply stabilizing device and then applied to a control circuit (which is hereinafter referred to as a CPU) and a transmission control circuit (which is hereinafter referred to as an LSI) for transmitting a transmission signal with respect to a transmission line (which is hereinafter referred to as a bus) under the control of the CPU. The CPU and LSI are set into the starting condition and initialized in response to application of the voltage so as to be ready for reception of a transmission signal from the bus.
An amplitude detection (which is hereinafter referred to as WU) circuit is started in response to application of a voltage from the power supply and detects transmission of a transmission signal from the bus connected thereto based on variation in the amplitude of the signal. When the transmission signal is detected, the power supply stabilizing device is controlled to be set into the operative state so that application of a voltage to the CPU and LSI becomes possible. Further, when transmission of the transmission signal is terminated, the WU circuit controls the power supply stabilizing device to set the same into a non-operative state and thus the current consumption of the battery is reduced by interrupting application of the voltage.
However, in the above current consumption control device, since an unstable voltage is applied to the WU circuit from the power supply, it is necessary to separately provide a stabilizing circuit for stabilizing the voltage. Further, it is necessary to connect a control device having a function of turning on/off the power supply voltage to the power supply stabilizing device. Therefore, with the above current consumption control device, the manufacturing cost will become high. Further, in general, since a capacitor having a large capacitance is inserted into a load of the stabilizing power supply, the rise time of the voltage becomes long. In addition, since the CPU is initialized, the rise time, that is, a period of time from the time that the signal is detected by the WU circuit until the CPU and LSI are correctly operated, will become long.